Taste and Smell Summary

Overview of Taste (Gustation)

  • Taste evolved to distinguish food from toxins.

  • Basic tastes: salt, sour, sweet, bitter, umami.

  • Innate preferences: prefer sweetness, reject bitterness.

  • Perception influenced by chemistry, combinations of tastes, and other senses.

Organs of Taste

  • Taste organs: tongue, palate, pharynx, epiglottis.

  • Tongue sensitivity varies (tip for sweetness, back for bitterness, sides for salt/sour).

  • Papillae types: foliate, vallate, fungiform; each contains taste buds (2000-5000 per person).

Taste Receptor Cells

  • 50-150 taste receptor cells per taste bud.

  • Taste cells undergo constant regeneration (~2 weeks).

  • Taste transduction involves ion channels & secondary messengers.

Mechanisms of Taste Transduction

  1. Direct passage through ion channels (salt & sour).

  2. Block ion channels (sour & bitter).

  3. Open ion channels by binding (some sweet).

  4. Activate second messengers (sweet & bitter).

Neural Coding of Taste

  • Based on response patterns of taste cells and gustatory axons.

  • Involves broadly tuned neurons and population coding for specificity.

Overview of Smell (Olfaction)

  • Smell identifies foods, enhances enjoyment, warns of danger.

  • Practice improves olfactory acuity (e.g., perfumers).

Organs of Smell

  • Mediated by olfactory epithelium in nasal cavity.

  • Contains olfactory receptor cells (neurons), supporting cells, basal cells.

Olfactory Transduction

  • Odorants bind to receptors, activate G-proteins, and initiate cyclic AMP signaling.

  • Leads to depolarization and generation of action potentials.

Central Olfactory Pathways

  • Olfactory tract connects directly to cerebral cortex, influencing emotions and memory.

  • Parallel pathways for discrimination, perception, motivation, feeding, and memory.

Coding of Neural Information

  • Spatial coding through receptor populations mapping odorants.

  • Possible temporal coding based on activity patterns in olfactory neurons.